Extruders of rigid PVC compounds and other thermoplastic compounds are constantly seeking ways to increase output rates through the purchase of larger extrusion equipment, the redesign of existing equipment or the redesign of formulations using new or improved additives. Improved output rates result in more economical plant operations that lead to greater profitability for the thermoplastic converters.
Thermoplastic formulations contain a variety of additives, including process aids (both conventional and lubricating), and internal and external lubricants, designed to increase throughput. Typically external lubricants and certain types of process aids, generically described as lubricating process aids, may reduce melt viscosity in PVC formulations. External lubricants, which are not soluble in the PVC formulation, coat the metallic surfaces of extrusion equipment allowing the PVC compound to slide thru the extruder, and in reality may have little affect on actual torque reduction of the compound. Reductions in “apparent torque” may be achieved by increasing external lubricant levels, however, over-lubrication using external lubricants can result in a variety of problems, from plate-out to deterioration of the extruded articles' physical properties. Lubricating process aids are typically low molecular weight polymers that have a lubricating function built into the polymer backbone. Their molecular weight approximates that of the PVC resin so torque reduction is not a function of dilution, but rather an interaction among the process aid and the rest of the formulation. Lubricating process aids typically have little affect on the physical properties of the extruded article. Generally, today's rigid PVC formulations are run without lubricating process aids. Conventional process aids are typically used in rigid PVC formulations. These typical process aids are high molecular weight polymers, with molecular weights significantly higher than PVC resin and cause increases in melt torque depending on their molecular weight.
There is a need for a process aid that reduces the extrusion torque of rigid thermoplastic formulations resulting in higher through-put.
Surprisingly, it was found that the use of an optimized lubricating process aid, having narrow ranges of methyl methacrylate, butyl acrylate and styrene, was shown to significantly reduce melt process torque in rigid PVC formulations, allowing converters of these materials to improve output rates